Monitoring natural triggering mechanisms of quick clay landslides

In 2021 the Norwegian Public Roads Administration (NPRA) initiated a project that aims to develop a new method for mapping and monitoring of quick clay hazards that affect our roads. The method is a pragmatic approach to evaluation of stability, where emphasis is given to qualitative assessment of slope stability, rather than quantitative methods such as stability calculations. Central to the methodology is emphasizing natural triggering mechanisms of quick clay landslides and assessing the extent to which they are present in an area. The method is based on elements from the Norwegian Water Resources and Energy Directorate (NVE) hazard classification of quick clay zones, while also drawing inspiration from an approach developed by the Ministère des Transports et de la Mobilité durable in Quebec, Canada (MTQ). The primary governing factors in this approach are to look for possibility of active erosion, earlier landslide activity and slope geometry. As part of the methodology, the project has developed a GIS (geographical information system) analysis to identify critical slopes with regards to height and inclination. In 2022 NPRA, NVE and the Geological Survey of Norway (NGU) collaborated on a field test which purpose was to test and assess the suitability of GIS analyses to identify possible triggering locations for quick clay landslides. A GIS analysis developed by NVE detects changes in the landscape from one year to another, while GIS analyses developed by NGU monitor fluvial erosion and local relief at the bottom of slopes. The field test showed that the new GIS analyses provided a highly accurate picture of slope activity in the investigated ravines. By assessing active erosion, landslide activity and slope geometry we aim to work more proactively, by systematically and efficiently prioritizing which areas need more detailed mapping, monitoring or security measures. GIS analyses will be used as a tool to help in measuring these factors in the many thousand quick clay areas in Norway.